1. Field of the Invention
The present invention relates to surface acoustic wave filter devices and duplexers, and in particular relates to a surface acoustic wave filter device including a plurality of longitudinally coupled resonator-type filters and to a duplexer including such a surface acoustic wave filter device.
2. Description of the Related Art
A surface acoustic wave filter device of the related art is disclosed in International Publication No. 2006/049000 for example. In International Publication No. 2006/049000, a configuration is disclosed in which 5-interdigital transducer (5-IDT) longitudinally coupled resonator-type surface acoustic wave filters are cascade connected to each other in two stages.
There is a problem with the surface acoustic wave filter device in which 5-IDT longitudinally coupled resonator-type surface acoustic wave filters are cascade connected in two stages in that, compared with a configuration in which 3-IDT longitudinally coupled resonator-type surface acoustic wave filters are cascade connected to each other in two stages, a ripple is generated inside the passband and spurious is generated in the vicinity of the passband.